Twisted flat bars gained by twisting a flat bar have such a form as shown by the symbol 6 in FIG. 17, for example, and iron, aluminum, stainless steel and the like are used as the material for the bar.
These twisted flat bars are buried in the ground and used as an anchor in order to secure a structure, such as a bench and a sign, to the ground, and in recent years, have been used as a foundation pile for forming a support or the like of a large building, as a part that forms a conveyance mechanism of a conveying apparatus, as shown in Patent Documents 1 and 2, and furthermore, as an ornament inside and outside a building.    Patent Document 1: Japanese Unexamined Patent Publication H10 (1998)-61742    Patent Document 2: Japanese Unexamined Patent Publication 2001-136844
A manufacturing method for such a twisted flat bar is disclosed in Patent Document 3, where a flat bar (5) is first attached to a fixture (2) attached to the output axis of a motor A (1) and a fixed dolly attached to the rod of a hydraulic cylinder (3), as shown in FIG. 17. Then, the motor is driven in such a state that a tensile force is applied to the hydraulic cylinder. Thus, the flat bar is twisted in such a state that a constant tensile force is applied so that a twisted flat bar can be manufactured. Here, the entire length of the completed twisted flat bar is slightly shorter than the entire length of the original flat bar. It is possible to manufacture a twisted flat bar up to a length of 6 m according to this method used for manufacturing by the present applicant.
Patent Document 3: Japanese Unexamined Patent Publication H10 (1998)-296342
However, the pitches of conventional twisted flat bars have different dimensions when measured precisely though the pitches look uniform when viewed visually, and when such a twisted flat bar is used as a feeding screw in a conveying apparatus, as shown in Patent Documents 1 and 2, the nut is caught by the twisted flat bar due to the inconsistency in the pitch, and thus, a problem arises such that it is difficult to move the nut relative to the twisted flat bar.
In addition, in the case where a number of twisted flat bars are aligned in parallel and used as a wall ornament or the like, a subtle inconsistency in the pitches can be clearly seen, which causes great damage aesthetically.
The reasons why these pitches are not uniform are (1) the material of the flat bar is inconsistent, and (2) it is difficult to apply a uniform twisting force throughout the entirety of the flat bar when the twisted flat bar is long in accordance with the method in which the two ends of the flat bar are held and twisted, as in Patent Document 3. In particular, when the twisted flat bar is long, sometimes the above described two reasons both contribute, which makes it extremely difficult to manufacture a long, twisted flat bar with uniform pitches.